Adding _.once ... Issue #121

test/functions.js

@@ -109,12 +109,11 @@ $(document).ready(function() {
   });
 
   test("functions: once", function() {
-    var addBang = function(str) { return str + "!"; };
+    var num = 0;
-    hi = "Hi";
+    var increment = _.once(function(){ num++; });
-    hi2 = _.once(addBang, hi);
+    increment();
-    hi3 = _.once(addBang, hi);
+    increment();
-    equals(hi2, "Hi!");
+    equals(num, 1);
-    equals(hi3, undefined);
   });
 
   test("functions: wrap", function() {

underscore.js

@@ -475,16 +475,16 @@
     return limit(func, wait, true);
   };
 
-  // Runs a function only if it's never been run before.
+  // Returns a function that will be executed at most one time, no matter how
+  // often you call it. Useful for lazy initialization.
   _.once = function(func) {
-    if (_.indexOf(onceRunFunctions, func)) {
+    var ran = false, memo;
-      onceRunFunctions.push(func);
+    return function() {
-      return func.apply(func, slice.call(arguments, 1));
+      if (ran) return memo;
-    }
+      ran = true;
-  }
+      return memo = func.apply(this, arguments);
-  
+    };
-  // Internal record of functions that have been run via `_.once`.
+  };
-  var onceRunFunctions = [];
 
   // Returns the first function passed as an argument to the second,
   // allowing you to adjust arguments, run code before and after, and